1. Field of the Inventions
The present inventions relate to a steering device for marine propulsion systems, and more particularly, to an electric type steering devices for outboard motors.
2. Description of the Related Art
Some known steering devices for outboard motors, such as those for steering a plurality of outboard motors, for instance, are the type disclosed in Japanese Patent Documents JP-B-2734041 (FIG. 1) and JP-A-Hei 8-276896 (FIG. 2).
In the steering system disclosed in Japanese Patent Documents JP-B-2734041, two outboard motors are steered by one steering wheel in the associated steering device. This steering device is constructed with a connecting member for connecting the outboard motors together so that steering movements of both the outboard motors are linked together and wires and the like for transmitting a steering force from the steering wheel are connected to this connecting member.
Two outboard motors, which can be controlled with a steering device such as the type disclosed in Japanese Patent Documents JP-B-2734041, as shown in FIG. 16(a), are configured such that the rotational directions of propellers 100 are opposite to each other. In common outboard motors, it is known that, when the propeller 100 rotates in water, a force F pushing the propeller 100 in a horizontal direction is produced due to a difference between the water pressures applied on the propeller 100 from above and below a propeller shaft 101, as illustrated in FIG. 16(a).
These forces F in the horizontal directions are, as shown in FIG. 17(a), cancelled when two outboard motors 102 are arranged such that the rotational directions of their propellers 100 are opposite to each other and are connected together by a connecting member 103. That is, with this configuration, transmission of the force F to the steering wheel is prevented.
The steering device for outboard motors disclosed in Japanese Patent Document JP-A-Hei 8-276896 (FIG. 2) is configured such that one of the two outboard motors connected together by the mentioned connecting member is steered by a hydraulic pressure (oil) cylinder. This oil cylinder is connected to a master cylinder provided on the steering wheel via a hydraulic pressure circuit.
This connecting member disclosed in Japanese Patent Document JP-A-Hei 8-276896 connects a steering bracket of each outboard motor to each other. This connecting member is constructed such that a plurality of links is combined to prevent an application of an excessive force on the connection part between the outboard motors and the connecting member when a trim angle of one of the outboard motors is changed to an angle different from the angle of the other outboard motor.
In the steering devices for outboard motors disclosed in Japanese Patent Documents JP-B-2734041 (FIG. 1) and JP-A-Hei 8-276896 (FIG. 2), members for connecting the steering wheel side and the outboard motor sides (wires and hydraulic pipes) need to be made to conform with the shapes and sizes of hulls. This kind of problem is solved by a use of an electric motor as an actuator for steering an outboard motor.
For example, There is a steering device for an outboard motor with an electric motor, for example, the one described in Japanese Patent Document JP-B-2959044 (FIG. 3). In this steering device, one outboard motor is steered by an electric motor. In this configuration, rotation of the electric motor is converted into reciprocating motions by a rack and pinion, and the reciprocating motions are transmitted to a steering bracket of the outboard motor. The electric motor is connected to a control device, and rotations of this electric motor are controlled to correspond to the rotational direction and rotating angle of the steering wheel by the control device.
Because the steering wheel side and the outboard motor side can be connected by electric wires in an electric type steering device for outboard motors configured in such a manner, its installation is easier comparing with the case that wires and hydraulic pipes and the like for mechanically transmitting steering forces are used.
In the case that a plurality of outboard motors is steered by the electric type steering device described in Japanese Patent Document JP-B-2959044 (FIG. 3) mentioned above, it is desirable to use a plurality of electric motors for high durability and reliability.
In the case that a plurality of outboard motors is steered by a plurality of electric motors, the motor, rack and pinion of the steering device is installed on each outboard motor.